The present invention relates to temporary road surfaces and, in particular, to a machine for assembling temporary road mats.
Temporary road mats are used extensively to allow vehicles and equipment to reach locations not serviced by permanent roads, particularly under conditions where ground surface would not support the traffic or where the temporary nature of use does not warrant the time and expense of a permanent road. The mats are generally constructed in multiple layers of heavy wood timbers in crisscrossing layers. The mats may also be provided with interlocking joints for connecting with adjacent mats as disclosed in U.S. Pat. No. 4,462,712 to Penland; U.S. Pat. No. 5,032,037 to Phillips et al.; and U.S. Pat. No. 4,889,444 to Pouyer. Commonly, each layer is nailed to the underlying layer. The final layer is fastened with extended length nails having protruding tips that crimped over to secure the assembly as disclosed in U.S. Pat. No. 5,234,204 to Hunt. The manual assembly, even with air powered nailing guns is time consuming and tiring and prone to misalignments.
Various assembly devices have been proposed for more accurately aligning the timber layers prior to nailing. U.S. Pat. No. 4,922,598 to Pouyer discloses an assembly table having an array of alignment stops for assisting positioning the timbers prior to nailing. U.S. Pat. No. 5,234,204 to Hunt, referenced above, discloses a dual stage assembly table facilitating nailing on opposite sides of the mat. Crimped extended length nails are used on the final layer to resist a lifting of the nail heads that can damage vehicle tires.
The nailing of the timbers also precludes convenient repair and replacement of damaged timbers. Typically, the mat must be substantially disassembled to access and replace damaged members. Such limitations have been overcome by the use of bolted mat configurations. Therein, holes are drilled at the intersections of the crossed timbers for receiving threaded fasteners. The resulting construction provides a smooth upper surface free of protruding nail heads. When replacement of a member is required, only the fasteners in the affected area need to be removed to allow substitution. Notwithstanding the advantages of the bolted construction, production rates, even with fixtures and assembly tables, have been limited by the cycle times of the serially required operations.
The present invention provides an improved method for making bolted temporary road mats wherein an assembly line includes a pair of in-line, phase opposed multilevel assembly tables supplied with precut timbers from conveyor systems including a trimming station. The precut timbers are oriented into multiple layers of mutually perpendicular timbers atop the table. A mobile gang drill carrying a plurality of drill heads travels along rails at the sides of the assembly tables and sequentially drills through holes at each lateral row of timber intersections. Carriage bolts are inserted downwardly through the drilled holes as completed. At lower bays beneath the assembly tables, nuts are assembled on the bolts to provide a unitized assembly. During the drilling at the first table, another mat is assembled at the other table. Following completion at the first table the gang drill indexes to the second table and performs the drilling sequence thereat, while the bolts are fastened at the first table. The gang drill alternates between the tables, with upper and lower crews transferring between tables for continuity and efficiency.
In one aspect of the invention there is provided an improved apparatus for making temporary road mats of bolted construction characterized by multiple layers of mutually perpendicular elongated timbers having an array of vertical intersections comprised of longitudinally spaced lateral rows, wherein said apparatus comprises: a pair of assembly tables spaced along an assembly line of a work floor, each of the tables having an upper layout surface spaced vertically above the work floor and providing a work bay therebelow, said layout surface having indicia for orienting the discrete timbers in each layer whereby said timber may be roughly assembled thereon into said layers with said intersections; a gang drill assembly supported for controlled movement in a longitudinal path along said assembly line with respect to said pair of assembly tables, said gang drill assembly carrying a plurality of drill units above said layout surface aligned for drilling the lateral rows of intersection; means for aligning said drill units at said lateral rows and for downwardly moving said drill units to form through holes through said timbers at said intersections subsequent to which bolts are inserted into said through holes from above said layout surface and fasteners are connected with said bolts in said work bay, the movement of said gang drill assembly and the sequence of said drilling being alternated between said assembly tables.
Accordingly, it is an object to provide an improved temporary road mat having threaded fasteners releasably interconnecting the various components.
A further object is to provide an improved apparatus for assembling temporary road mats wherein rough timbers are feed on a conveyor system through a trimming station to provide precut timbers to a pair of spaced assembly tables for positioning into multiple crossed layer orientation and a longitudinally positionable multiple drill assembly alternately drills fastener holes in the timbers at each table.
Another object is to provide an apparatus for assembling bolted temporary road mats wherein a gang drill assembly is used to simultaneously drill lateral rows of through holes for receiving fasteners for interconnecting the mat components.